From the Guidelines
A left shift in white blood cells (WBCs) is identified by examining a complete blood count (CBC) with differential, specifically looking for an increased percentage of immature neutrophils (bands, metamyelocytes, myelocytes) in peripheral blood, with a left shift defined as a percentage of band neutrophils or metamyelocytes ≥ 16% or a total band neutrophil count ≥ 1500 cells/mm³, as recommended by the Infectious Diseases Society of America 1. To identify a left shift, look for the following key indicators:
- An increased percentage of band neutrophils or metamyelocytes
- A total band neutrophil count ≥ 1500 cells/mm³
- The presence of even more immature forms like metamyelocytes The laboratory report will typically flag these abnormalities, often using terms like "left shift," "bandemia," or "immature granulocytes present." This finding indicates active bone marrow response to infection or inflammation, as the body increases neutrophil production faster than cells can fully mature. Left shifts commonly occur with bacterial infections, tissue damage, inflammatory conditions, and certain malignancies. The degree of left shift often correlates with infection severity, making it a valuable diagnostic indicator that helps guide treatment decisions, particularly regarding antibiotic therapy. It is essential to perform a complete blood cell (CBC) count, including peripheral WBC and differential cell counts, for all residents who are suspected of having infection within 12–24 h of onset of symptoms, as recommended by the Infectious Diseases Society of America 1.
From the Research
Identifying Left Shift on WBC
To identify a left shift on a white blood cell (WBC) count, several parameters can be evaluated, including:
- Neutrophil band count: This is the percentage of immature neutrophils (bands) in the blood, which can indicate an increase in neutrophil production in response to infection or inflammation 2, 3, 4.
- Immature to total neutrophil (I/T) ratio: This ratio can help identify an increased demand for neutrophils, which may indicate bacterial infection 2, 3.
- Morphologic changes in neutrophils: The presence of toxic granules, Döhle bodies, and cytoplasmic vacuoles can indicate a response to infection or inflammation 2, 4.
- White blood cell count: An increase or decrease in WBC count can indicate infection or inflammation, and when combined with left shift data, can provide a more accurate evaluation of patient condition 5, 6.
Evaluation Methods
Different methods can be used to evaluate left shift, including:
- Microscopic examination of a blood smear to determine the percentage of band neutrophils and identify morphologic changes 2, 4.
- Automated hematologic analyzers, which can provide a left-shift flag or calculate the I/T ratio 2.
- Manual 100-cell differential counts, which can be repeated at regular intervals to monitor changes in WBC count and left shift over time 6.
Clinical Applications
Identifying left shift on a WBC count can be useful in:
- Diagnosing bacterial infections: A combination of WBC count and left shift data can help identify the presence and severity of infection 5, 6.
- Monitoring patient condition: Regular evaluation of WBC count and left shift can help track the course of infection and response to treatment 6.
- Identifying high-risk patients: An elevated I/T ratio or presence of morphologic changes in neutrophils can indicate a high risk of depletion of marrow neutrophil reserves and death from sepsis 3.